The present invention relates to an optical disc and to a disc reproducing method for use in an optical disc apparatus. More specifically, the present invention pertains to an optical disc on which a predetermined identification or discrimination signal is recorded on each of a plurality of tracks, each track having a length equal to one revolution of the disc, within a predetermined region by a modulation system enabling these identification signals to be read when a tracking servo loop is open. The signals identify a type of servo tracking system (continuous or sample servo system) which may be used with the disc. The invention further relates to a disc reproducing method for opening the tracking servo loop when a pick-up traverses the plurality of tracks, synthesizing or combining the reproduced signals from the plurality of tracks on the disc in a single-track-reproducing manner, and treating these signals as a single continuous signal.
It is well known that there are two kinds of optical discs. One kind of disc has a track or groove continuously formed on the disc and the information is recorded in the groove or on the land formed between adjacent helical circumferential portions of the groove. As with compact optical discs and optical video discs, the optical disc of the present invention is controlled by a continuous tracking method in accordance with a push-pull principle, for example.
In another kind of optical disc, wobble pits are formed a fixed distance apart on the optical disc. These wobble pits are arranged to the left and right respectively, of track centerline (virtual track) to produce a tracking error signal by using the difference in RF signal levels produced when the respective wobble pits are read. Each tracking error signal is held until the disc rotates to the positions of the next wobble pits.
Conventionally, there is no groove on an optical disc containing a sample-servo which is used for track centering and there are no wobble pits on an optical disc which is used in a system which has continuous tracking control. Accordingly, an optical disc for an apparatus having a continuous tracking control system cannot be driven in an optical disc apparatus employing a sample-servo control system. Conversely, an optical disc for an apparatus having a sample-servo system cannot be driven in an optical disc apparatus employing a continuous tracking control system. Thus, it is necessary to identify the system with which the optical disc apparatus is to be used before using the disc with a particular apparatus.
In accordance with known approaches, an identification opening or hole has been made in a case accommodating an optical disc to identify the kind of operating system with which the disc is to be used. Consequently, it is necessary to make two kinds of cases for different discs, resulting in a high manufacturing cost.